In all the report about the latest development of communication techniques, next generation network (NGN) and 3rd generation (3G) mobile communication have become two focuses recently.
The definition of the NGN keeps changing during its development. At “2004 Global NGN Summit Forum” hosted by International Telecommunication Union (ITU), the standard of NGN is defined as a packet-based network capable of providing various services including telecommunication service and using transmission techniques supporting different bandwidths and having quality of service (QoS) assurance. The final development direction and scope of the NGN is thus determined.
Judging from the deployment of the NGN, two key components are adopted by the NGN for networking: a media gateway control controller (MGC) and a media gateway (MG). The MGC is responsible for the function of calling control. The MG is responsible for the function of service bearing so as to implement the separation of the calling control plane and the service bearing plane. The two can involve independently so that it is possible to fully share the network resources, simplify equipment upgrade and service expansion, and greatly reduce the cost of development and maintenance.
Media gateway control protocol is a main protocol for the communication between an MGC and an MG. Currently the widely used protocols are gateway control protocol/H.248 (H.248/MeGaCo) and media gateway control protocol (MGCP). The communication protocol between MGs is real-time transfer protocol (RTP) as shown in FIG. 1.
The H.248/MeGaCo protocol version 1 was established by the IETF and the ITU jointly in Nov., 2000 and revised in Jun., 2003. The H.248/MeGaCo protocol version 2 was established by the ITU in May, 2002 and revised in Mar., 2004. The H.248/MeGaCo protocol version 3 was issued by the ITU in Sep., 2005.
Regarding the H.248/MeGaCo protocol, there are 8 basic commands between the MGC and the MG as follows: Add, Modify, Subtract, Move, AuditValue, AuditCapabilities, Notify, and ServiceChange.
In the H.248 protocol, the MG implements the service bearing through the resources on it. The resource is abstractly represented as a Termination. The Termination is further classified into a Physical Termination and an Ephemeral Termination. The former represents some semi-permanently existing physical entity such as time division multiplexing (TDM) channels. The later represents some ephemerally applied public resources released after being used, such as RTP flows. The combination among Terminations is abstractly represented as Context including many Terminations. Therefore, Topology is always used to describe the mutual relationship between Terminations. A Termination not associated with other Terminations may be included by a special Context called Null Context.
In such an abstract model based on the H.248 protocol, connection of a call lies actually in operations of Terminations and the Contexts. The operations are completed through the command requests and responses between the MGC and the MG. Command parameters, also called Descriptor, are classified into Property, Signal, Event and Statistic. The parameters with service pertinency are logically aggregated into a Package.
Specifically, the Property represents the specification of resource requirements. It is usually issued by the MGC to the MG or is set by the MG itself, for example, maximum or minimum value set by a jitter buffer.
The Signal is used by the MGC to instruct the MG to perform resource operation, for example, play a dial tone, a ring back tone, a busy tone to users.
The Event is used by the MGC to instruct the MG to monitor status, for example, monitor the user's Off-hook, On-hook, Dialing, Flash-hook.
The Statistic represents the utilization status of the resource on the Termination or Stream. Generally, the MG performs calculation operation. The MGC may optionally perform Enable or Disable, i.e. Activate or Deactivate some of the parameters, such as current value or average value applied by a jitter buffer, accumulation statistics of time length, accumulation statistics of the number of sent or received byte, accumulation statistics of the number of sent or received packet, statistics of packets current loss rate, statistics of current value of receiving jitter, statistics of current value of transmission delay, statistics of accumulation discarding rate of network packets, statistics of accumulation discarding rate of jitter buffer. According to the requirement of QoS monitoring and controlling, more statistic parameters may be extended such as those about packet loss rate with a time period, maximum, minimum or average value of delay or jitter.
The current H.248 protocol regulates that the collection, calculation and recording of information relevant to the statistic parameter are actually operated by the MG. The MGC can only perform Enable or Disable besides that the MGC can obtain the value of the parameter by Audit. It can be seen that, the MGC only has the ability to obtain the result of the statistic parameter operated by the MG but the MGC does not have the ability to intervene the operation control process. Typically, the MGC does not have the mechanism to dynamically adjust the value of some statistic parameter in service, i.e. in enabled or active status into a standard value.